1. Field of the Invention
The present invention relates to a controller of an injection molding machine having an abnormality detection unit of a voltage detection unit.
2. Description of the Related Art
An injection device and a mold clamping device in an injection molding machine are driven using servomotors, and it is general that drive power is supplied to the servomotors from a drive device of a motor to drive a screw and a movable platen back and forth. Here, in the injection device, it is necessary to move the screw back and forth at high speed, and in the mold clamping device, it is necessary to move the movable platen which supports a mold back and forth at high speed. Therefore, large electric power is required.
When the servomotor is driven with high output, it is necessary to supply large electric power to the servomotor from an amplifier. Especially in the case of high speed injection for molding a thin article and in the case of high speed clamping for compression molding, although time during which the motor operates at high speed is short, since large electric power is temporarily supplied to the motor, there is concern that a power supply device becomes large in size. To solve this problem, it is known that a DC voltage unit of a drive device which drives the servomotor is provided with an electric storage unit, voltage of the electric storage unit is boosted to store energy which is necessary at the time of high speed operation, thereby preventing the power supply device from becoming large.
Japanese Patent Application Laid-Open No. 2000-141440 A discloses a technique in which regenerative electric power generated by a motor is stored in an electric storage unit during a deceleration period of the motor and the electric power stored in the electric storage unit is supplied to drive power side during an acceleration period of the motor. Japanese Patent Application Laid-Open No. 2012-240199 A discloses a technique in which a power supply converter is operated in a normal direction only for a predetermined period in a molding cycle of an injection molding machine so that voltage between two poles of DC link becomes equal to predetermined target voltage.
In any of the techniques, a voltage detecting circuit detects voltage of the electric storage unit, and output of the power supply converter is controlled such that the detected voltage becomes equal to the target voltage. At this time, if it is not possible to normally detect voltage due to trouble of the voltage detecting circuit, there is concern that voltage of the electric storage unit becomes overvoltage. For example, when voltage cannot be detected normally and voltage which is lower than actual voltage is detected, there is concern that although the actual voltage is higher than the target voltage, supply of electric power to the electric storage unit is continued and as a result, voltage of the electric storage unit becomes overvoltage.
To prevent this problem, it is possible to take methods of providing a preliminary voltage detecting circuit or providing an overvoltage preventing circuit, but since these methods require to provide an additional circuit, there is concern that costs are increased.